This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 2001-308931, filed Oct. 4, 2001; No. 2001-308932, filed Oct. 4, 2001; and No. 2002-084215, filed Mar. 25, 2002, the entire contents of all of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a nonlinear dispersion-shifted optical fiber generating a nonlinear optical phenomenon relative to input light as well as an optical signal processing apparatus and a wavelength converter each using the particular optical fiber.
2. Description of the Related Art
The nonlinear optical phenomena that can take place within an optical fiber include, for example, four wave mixing, self phase modulation, cross phase modulation, and stimulated Brillouin scattering. If these phenomena take place within an optical fiber, wavelength conversion, phase modulation, scattering, etc., are generated, increasing the noise component or inhibiting a sufficient transmission of the input light. Such being the situation, it was attempted to exclude these nonlinear optical phenomena as much as possible in a conventional optical fiber for transmission.
In recent years, the conventional concept has been changed so as to carry out wavelength conversion, in which the wavelength of an optical signal is changed from the long wavelength side toward the short wavelength side, and optical signal processing such as waveform correction for correcting the distortion of the waveform of the optical signal by positively utilizing nonlinear optical phenomena.
However, since it was attempted to exclude nonlinear optical phenomena as much as possible in the past, as described above, it is impossible to obtain an optical fiber suitable for carrying out optical signal processing such as wavelength conversion by positively utilizing nonlinear optical phenomena.
A nonlinear optical fiber for carrying out wavelength conversion is disclosed in, for example, Re-published Patent No. WO 99/10770. However, the nonlinear optical fiber disclosed in this prior art is not necessarily sufficient. For example, it has been clarified that, if it is intended to increase the nonlinearity, it is difficult to adjust the chromatic dispersion, making it difficult to manufacture the optical fiber.
Also, in order to utilize positively the nonlinear optical phenomena of the optical fiber, it is desirable for the optical fiber to have a desired dispersion value at the wavelength of the input light. Particularly, in order to utilize wavelength conversion, it is desirable for the optical fiber to have a zero dispersion wavelength in the vicinity of the wavelength of the input light. However, when it comes to a nonlinear optical fiber, in which it is difficult to adjust the zero dispersion wavelength, it is laborious to manufacture a plurality of different kinds of optical fiber differing from each other in the zero dispersion wavelength corresponding to the wavelength of the input light for carrying out optical signal processing of, for example, the wavelength multiplex transmission light.
An object of the present invention is to provide a practical nonlinear dispersion-shifted optical fiber, which is suitable for wavelength conversion or optical signal processing utilizing nonlinear optical phenomena and which can be manufactured easily.
Another object of the present invention is to provide an optical signal processing apparatus using the optical fiber noted above.
Further, still another object of the present invention is to provide a wavelength converter using the optical fiber noted above.
According to a first aspect of the present invention, there is provided a nonlinear dispersion-shifted optical fiber, wherein a chromatic dispersion at a wavelength of 1550 nm is equal to a set value required for optical signal processing utilizing a nonlinear phenomenon, a dispersion slope at a wavelength of 1550 nm falls within a range of 0.001 to 0.1 ps/nm2/km, a margin of fluctuation of the chromatic dispersion in a longitudinal direction of the optical fiber at a wavelength of 1550 nm falls within a range of 0.01 to 3 ps/nm/km, and a nonlinear constant n2/Aeff at a wavelength of 1550 nm is not smaller than 15xc3x9710xe2x88x9210/W.
According to a second aspect of the present invention, there is provided a nonlinear dispersion-shifted optical fiber, comprising a first core having a refractive index higher than that of a clad, a second core formed on a periphery of the first core and having a refractive index lower than that of a clad, and a clad formed on a periphery of the second core and having a refractive index substantially equal to that of pure silica, wherein an outer diameter D1 of the first core falls within a range of 3 to 8 xcexcm, and a ratio D1/D2 of the outer diameter D1 of the first core to an outer diameter D2 of the second core falls within a range of 0.3 to 0.85.
According to a third aspect of the present invention, there is provided an optical signal processing apparatus comprising the nonlinear dispersion-shifted optical fiber noted above.
Further, according to a fourth aspect of the present invention, there is provided a wavelength converter comprising the nonlinear dispersion-shifted optical fiber noted above.
Additional objects and advantages of the present invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the present invention. The objects and advantages of the present invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.